Remote hydraulic control systems have numerous applications for controlling hydraulic jacks and hydraulic motors which may, for example, be used to operate a wide variety of devices from earth moving equipment such as power shovels, loaders, bulldozers, and the like, to devices such as lifts and "cherry pickers". In use, it is frequently desirable to provide rapid response times. In some applications, long control lines from hydraulic remote controllers are utilized These control lines can exceed 50 ft. With long control lines, control response times become slow. In cold weather, control response times decrease further for outside applications.
The prior art does not recognize the phenomenon of slow response times for relatively long control lines, nor does the prior art suggest a solution to the problem inherent in utilizing long control lines.
In devices of interest with respect to the present invention, hydraulic jacks and motors are controlled by main control valves having valve spools which slide from a neutral position, determined by a positioning spring, to either a first or second operating position. When the valve spool is in the first position, the jack or motor advances or rotates in a first direction and when the valve spool is in the second position, the jack or motor advances or rotates in a second direction. The position of the valve spool is determined by a remote controller which may be operated manually to select which way the valve spool moves.
In prior art devices, pilot hydraulic fluid at relatively high pilot pressure is applied directly to opposite ends of the valve spool. This requires that a relatively large volume of pilot hydraulic fluid be transmitted. When a system requires a manual or other controller which is remotely displaced from a main control valve, the volume of pilot hydraulic fluid which must be displaced through control lines is necessarily increased because control lines are lengthened. When these lengths approach 50 feet or more, response times tend to increase due to the increased volume of pilot hydraulic fluid which must be transported. Since it is usually desirable to minimize response times in any situation, there is a need for an approach to provide minimized response times when control lines approach 50 feet or more in length.